Next-generation, affordable SO2 abatement for coal-fired power generation – A comparison of limestone-based wet flue gas desulphurization and Sulfacid® technologies for Medupi power station A. Strickroth1, M. Schumacher1, G.W. Hasse2, and I. Kgomo2 Affiliation: 1 Carbon Process & Plant Engineering S.A., Grand Duchy of Luxembourg, Europe. 2 EPCM Global Engineering (Pty) Ltd, Centurion, 0157, South Africa. Correspondence to: G.W. Hasse
Email:
gunther@epcm.co.za
Dates:
Received: 14 Jun. 2020 Revised: 14 Sep. 2020 Accepted: 15 Sep. 2020 Published: October 2020
How to cite:
Strickroth, A., Schumacher, M., Hasse, G.W., and Kgomo, I. Next-generation, affordable SO2 abatement for coal-fired power generation – A comparison of limestone-based wet flue gas desulphurization and Sulfacid® technologies for Medupi power station. Journal of the Southern African Institute of Mining and Metallurgy, vol. 120, no. 10, pp. 581–590. DOI ID: http://dx.doi.org/10.17159/24119717/1252/2020 ORCiD ID: G.W. Hasse https://orchid.org/0000-00034912--0305
Synopsis Coal is used to generate more than three-quarters of South Africa’s electricity, while numerous coal-fired boilers are employed for steam generation in industrial processes. However, coal-fired power generation is responsible for the release of the largest quantities of SO2 emissions to the atmosphere and leads to detrimental health and welfare effects in communities in the proximity of coal-fired plants. The classical industrial SO2 abatement solution for the coal-fired power generation industry is wet flue gas desulphurization, which uses a limestone adsorbent and produces a gypsum by-product (WFGD L/G). In South Africa, due to the poor quality of the limestone the gypsum product is unsaleable and is co-disposed with coal ash. In comparison, the Sulfacid® process technology converts SO2 contained in industrial flue gas into saleable sulphuric acid using a catalytic process requiring only water and air. This process does not require limestone. The scale of the latest commercial applications of the Sulfacid® SO2 abatement technology in the chemical, fertilizer, and copper mining industries demonstrates the potential and readiness of this technology to be employed in the coal-fired electricity and steam production sectors. This paper provides a first-order direct comparison between the techno-economic aspects of the WFGD (L/G) and Sulfacid® technologies using the requirements specified for the 6 × 800 MWe Eskom coal-fired Medupi power station. The results indicate that affordable flue gas desulphurization technology exists that could be adopted by the South African industry to reduce SO2 emissions to legislative limits and beyond. Keywords SO2 abatement, coal-fired power, and heat generation, sulphuric acid, wet fluidized gas desulphurization, Sulfacid®, waste-to-chemicals.
Introduction Coal-fired power generation in South Africa remains indispensable for maintaining economic activity now and into the foreseeable future, even with the introduction of renewable energy. During the period April 2018 to March 2019, approximately 77% of all electricity in South Africa was generated by 15 coal-fired power plants which, in addition to gas, hydro-, and nuclear power, formed part of a total of 92% Eskom-generated electricity supplied to the national grid (Stats SA, 2018a, 2018b, 2019; Eskom, 2019). Flue gas from coal-fired power plants contains sulphur dioxide (SO2) that originates from the sulphur in the coal, and which has detrimental health and welfare effects on communities living in the proximity to the plants. Sulphur is contained in coal predominantly as organic sulphur (S) and pyritic sulphur (Calkins, 1994), with typical total sulphur contents of 0.54% (by mass) for thermal export coal, > 1% for Sasol syngas production coal, < 2% for Eskom thermal power generation coal, and 2% (range 0.4–3.0%) for discard coal (Hall, Eslait, and den Hoed, 2011; Steyn and Minnitt, 2010; Makgato and Chirwa, 2017). During pulverized coal combustion, the organic and pyritic sulphur is converted mostly into SO2, and in small quantities into sulphur trioxide (SO3) (Müller, Schnell, and Scheffknecht, 2013), with only approximately 10% of the sulphur captured in the coal ash (Harrison, 2006). The SO2 flue gas concentration for Eskom power plants typically ranges from 1 623 mg/Nm3 (dry, 10% O2) for 0.7% S (air-dried basis) at Kriel power station to a maximum of 3 934 mg/Nm3 for 1.8% S at Medupi power station (Harris, 2014; Girmay and Chikobvu, 2017; Kolker, Senior, and Alphen, 2016). Likewise, the SO2 emissions for the Eskom coal-fired power plant fleet (single point sources) range from 26 Mt/a for Komati power station to 429 Mt/a for Matimba power station (van Geuns, 2018; Mathebula, 2017). Most of the Eskom coal-fired power stations are located in, and impact the air quality in, the Highveld and Waterberg Priority Areas (South Africa, 2007, 2012a, 2012b, 2015).
The Journal of the Southern African Institute of Mining and Metallurgy
VOLUME 120
OCTOBER 2020
581 ◀